Vast research work on visible-laser-based photoacoustic spectroscopy of NO₂ in air has been performed at the CEILAP. The study of the mechanisms of acoustical energy losses in a cavity is carried out exciting with a pulsed visible laser. For precise measurements a processing method is developed which allows obtaining high resolution of the photoacoustic signal spectrum when the acquisition window is limited. Devices are shown, where the resonant excitation is obtained with either a mechanically amplitude-modulated or an acousto-optically Q-switched green laser. A simpler, more compact and cheaper acquisition system is obtained through digitizing the pre-amplified signal by the sound card of a PC. The detection limit of different setups and an application to the measurement of the NO₂ content in car exhausts are presented. Moreover, a one-dimensional model for cell design and otimization of S/N ratio is developed. It is verified by measurements on NO₂ mixtures in a specially built acoustic cavity with a detached Helmholtz resonator.

Date Published: 21 October 2004
PDF: 6 pages
Proc. SPIE 5622, 5th Iberoamerican Meeting on Optics and 8th Latin American Meeting on Optics, Lasers, and Their Applications, (21 October 2004); doi: 10.1117/12.591016

Published in SPIE Proceedings Vol. 5622:
5th Iberoamerican Meeting on Optics and 8th Latin American Meeting on Optics, Lasers, and Their Applications
Aristides Marcano O.; Jose Luis Paz, Editor(s)